Photoshop is capable of batch-processing, too. Have a look at the Actions-palette.
I wouldn't assume everyone has PS- I made my comment before I knew he had PS.
IrfanView is simple and good at what it does. I've never batched anything in PS, so I can't compare. But IrfanView can resize, rename, move, copy, delete, change file type, filter, crop, resize, flip, rotate, add text, and change color depth on as many files as you need. You can even pick a "master folder" and it will operate on all files in all subfolders of that master folder.
Good stuff.